In general, a compressor-type refrigerator comprises a compressor, a condenser, an expansion valve and an evaporator, and a mixed liquid comprising a refrigerant and a lubricating oil is circulated in the closed system of the refrigerator. In the compressor-type refrigerator of that type, in general, dichlorodifluoromethane (R12), chlorodifluoromethane (R22) and the like have heretofore been used as refrigerants and various mineral oils and synthetic oils as lubricating oils.
However, since chlorofluorocarbons such as R12 mentioned above will bring about environmental pollution, as destroying the ozone layer existing in the stratosphere, their use is being severely controlled in all the world. Given the situation, new refrigerants, hydrogen-containing Flon compounds such as hydrofluorocarbons and hydrochlorofluorocarbons have become specifically noted. Since such hydrogen-containing Flon compounds, for example, hydrofluorocarbons such as typically R134a will not destroy the ozone layer and can be substituted for R12 and the like without almost changing or modifying the structure of conventional refrigerators, they are favorable as refrigerants for compressor-type refrigerators.
The properties of these new Flon-substituent refrigerants are different from those of the conventional Flon refrigerants; and it is known that refrigerator oils capable of being used along with these may comprise a base oil component selected from, for example, polyalkylene glycols, polyesters, polyol esters, polycarbonates and polyvinyl ethers having particular structures, and various additives to be added to said base oil component, such as antioxidants, extreme pressure agents, defoaming agents and hydrolysis inhibitors.
However, these known refrigerator oils are problematic in practical use in that, when used in the atmosphere comprising any of the above-mentioned refrigerants, their lubricating properties are poor and, in particular, they cause increased abrasion loss between aluminium materials and steel materials constituting the refrigerating parts in car air-conditioners and electric refrigerators. The sliding parts composed of such aluminium materials and steel materials are used, for example, in the combination of a piston and a piston shoe and in the combination of a swash part and its shoe part in reciprocating compressors (especially, in swash plate compressors), and in the combination of a vane and its housing part in rotary compressors, and they are important elements for lubrication.
On the other hand, various abrasion resistance improvers are known, but, at present, no means is known capable of effectively preventing the abrasion between aluminium materials and steel materials in particular conditions in such a Flon atmosphere without interfering with the stability of the parts composed of these materials.